Turbine jet engines may be utilized to power and/or to convey an aircraft, such as an airplane. Such turbine jet engines rely upon gas expansion, from combustion of a fuel, to provide a motive force for rotation of one or more compressors and/or turbines. As such, turbine jet engines may require a constant supply of fuel and may combust, or consume, the fuel continuously during operation thereof.
While turbine jet engines may be highly effective at generating thrust, there may be inefficiencies associated with operation thereof. As an example, the turbine jet engine must be sized for a maximum needed thrust, such as may be utilized during acceleration of an aircraft that utilizes the turbine jet engine, during take-off of the aircraft, and/or during an engine-out condition of the aircraft. As such, an operational efficiency of the turbine jet engine at constant, or cruise, speeds may be less than otherwise would be possible were the turbine jet engine sized for constant speeds. As another example, during deceleration of the aircraft, kinetic energy of the aircraft may be lost. As yet another example, during descent of the aircraft, potential energy of the aircraft may be lost. This lost kinetic and/or potential energy generally is not recovered and represents a loss of energy that initially was utilized to accelerate the aircraft and/or to attain a given altitude, respectively.
The above-discussed sizing constraints and/or energy losses represent inefficiencies in current turbine jet engine designs and are unaddressed by current hybrid engine designs. Thus, there exists a need for improved hybrid turbine jet engines and for methods of operating the improved hybrid turbine jet engines.